The present invention relates to a pressurized fluid driven device in general, and more particularly to such a device having a motor of the external rotor type.
There are already known various types of devices which are powered by a pressurized medium, such as compressed air or other gaseous medium, or by a hydraulic fluid. Among these, there are also known various devices which utilize, as a drive, a motor of the external rotor type, that is, a motor the rotor of which circumferentially surrounds and rotates about a stator. In the devices of this type, it is necessary to supply the pressurized medium into the rotor in order to drive the same into rotation, this being accomplished by providing channels in a stationary component of the device, which communicate with corresponding channels provided in the rotor across an interstice which is present between the stationary component and a rotating component of the motor.
One of the conventional devices of this type is a hand-held power tool, such as a compressed air power impacting tool which can be used for threading screws or nuts and for tightening the same. This conventional power tool utilizes a rotary motor of the vane type having an external rotor. The compressed air is delivered into the external rotor of this motor, which can rotate only in one direction, through an internal stator via an axial channel and via radial bores communicating with the axial channel, the radial bores communicating, across an interstice existing between the external rotor and the internal stator, with an annular groove provided in the external rotor. The compressed air passes through channels provided in the rotor, driving the rotor into rotation, and the spent air is directly discharged from the external rotor through bores which are provided in the power tool.
In this known power tool, the cylindrical interstice between the external rotor and the internal stator is made with as small a width as possible, and the axial length of the interstice is made as large as feasible, so as to minimize the leakage of the compressed air through the interstice, without performing useful work. The relatively small width and relatively large length of the interstice is the only means for preventing the compressed air from escaping through the interstice. Despite these expedients, considerable losses of the compressed air are encountered in this prior-art power tool.
The above-described problems encountered in the non-reversible power tool are even compounded when it is desired to so construct the power tool as to be reversible in its direction of rotation. Such reversible power tools are very useful and could be very compact and simple in construction when using a reversible motor of the external rotor type which is driven by compressed air or the like. However, under these circumstances, additional channels, radial bores and annular grooves have to be provided in the stationary and rotating components of the motor for rotating the rotor in a direction opposite to that in which it rotates when the above-discussed channels, bores and grooves are used. Under these conditions, it is not only necessary to seal the interstice between the first-mentioned annular groove and the exterior of the motor, but also to seal the interstice between the additional annular groove and the exterior of the motor and, in addition thereto, also the interstice between the two annular grooves. It will be appreciated that an attempt to minimize the escape of the compressed air through the interstice by making the same relatively long in the axial direction is bound to fail, at least for use in hand-held power tools, inasmuch as the axial dimensions of the entire power tool would then be excessive, and so would its weight, contrary to what is expected of hand-held power tools.